The invention relates generally to photographic exposure control system and, more particularly, to an exposure control system which is responsive to scene lighting in both ambient and flash modes of operation.
In U.S. Pat. No. 3,896,458, an automatic exposure control system responsive to scene light in ambient operation and additionally responsive to a subject distance in flash operation is described. In that arrangement, a shutter-diaphragm mechanism simultaneously defines two correlated aperture values respectively controlling the scene light emitted to both the film plane and the camera photocell.
In operation, the shutter-diaphragm is driven from a closed position through enlarging aperture values with the photocell aperture in a leading arrangement to the taking aperture so as to provide suitable anticipation of the final exposure value when the optical path is again blocked in accordance with a termination signal from the photocell network. For ambient operations, the correlation between the two aperture values is altered to provide relatively lower input to the photocell in compensation for the reduction in anticipation factor inherent with a long exposure interval. However, in flash operation, the shutter-diaphragm is halted at predetermined positions so as to select an operational aperture value in accordance with subject distance, preferably with camera focusing. For optimum film exposure, it is important to provide compatible operation of the photo-responsiveness in both modes of operation.
Consequently, it is an important object of this invention to provide an improved photographic exposure control system.
It is another primary object of this invention to provide an improved automatic exposure control system suitable for both flash and ambient illumination.
Still another object of this invention is to provide a shutter-diaphragm exposure control system responsive solely to scene brightness when operated in an ambient mode and responsive to both scene brightness and subject distance when operated in a flash mode.